Derating of transformers under non‐linear load current and non‐sinusoidal voltage – an overview

Abstract

The increasing application of non-linear loads in power system causes additional losses in transformers resulting in premature damage. Manufactures and users of transformers realise the importance of this phenomenon and it is vital to adopt a procedure to prevent it thereby enhancing the reliability of power system. To achieve this, the most common method is derating of transformers. This paper intends to review derating of transformers under nonsinusoidal operation, for which all available approaches are classified into four major methods including IEEE recommended, analytical, experimental and finite elements based method. For each method, the fundamental theory, significant factors related to derating, test techniques as well as advantages and disadvantages are discussed. The methods are then evaluated and compared with each other from different points of view. Moreover, the overall trend of a more precise derating method is suggested. This review clarifies the research areas which require attention in the future to advance the subject.

Demand Side Management Effects on Substation Transformer Capacity Limits

“…Derating distribution, industrial, or commercial transformers due to heating induced by harmonics distortion is a well-documented application [35][36][37][38][39]. As defined in Faiz, Ghazizadeh, and Oraee, the four methods applicable to derating transformers include IEEE recommendations, analytical methods, experimental approaches, and finite elements [14]. Depending upon the application, load type, and available transformer and system information, each approach possesses disadvantages and advantages.…”

“…With smart grid monitoring and switching capabilities, ensuring system balance between phases is achieved easier when compared to past systems. The transformer model applied in the research assumes the substation transformer serves a balanced load, which nullifies the disadvantage of applying the IEEE method for derating [14]. Analysis of this model with varying load profiles identifies the peak demand that produces internal transformer temperatures that meet the limits set forth by IEEE Std.…”

“…Aging is affected by the ambient temperature surrounding the transformer unit; therefore, varying weather conditions throughout the year may dictate seasonal capacity limits [14]. If a single limit is satisfactory, analysis is performed to identify the time of year when daily average ambient temperatures and load requirements produce the most extreme transformer aging and/or internal temperatures.…”

“…Integration of PV, ES applications, and EV charging requires the implementation of power electronics, which increase the harmonic distortion on the grid. The heat generated from harmonic distortion also contributes to the internal heating of a transformer, which increases aging and can thereby impact capacity limits [9,13,14]. Although there are equipment standards that limit the amount of harmonic distortion induced by a single device, system values exceeding IEEE Std.…”

Derating of distribution transformers under non‐linear loads using a combined analytical‐finite elements approach

“…All the above-mentioned references can be categorised into four groups [22]: the IEEE standards [2][3][4], experimental [6][7][8][9][10][11][12], analytical [13][14][15][16] and finite elements (FE) analysis [17][18][19][20][21]. The major problem with the IEEE standards is that the proposed assumptions ultimately lead to conservative results.…”